Stihl ms260 issues

[Welshfred]

I've been running 260s and previously 026s for decades now and never encountered this problem before. So the saw has been running fine. A bit slow to start and recently needing 2 choke on/off sequences to start but running really nice after that until this point. I use it for a tank no problem, come back an hour later and it won't run. Fires with the choke then fires without then dies whether you give it throttle or not. Dies faster if you do. Will only then restart with choke again, then fires without choke as you'd hope but dies. I found I can repeat this sequence again and again but still the saw won't run. Just dies with throttle. If you start it with the brake off it races for about 3-5 seconds then dies.

It feels like it's not getting enough fuel. Changed filter and spark plug, cleaned air filter, checked tank vent. No indication of leaks from the fuel hose. Discovered a leaking fuel tank cap, will replace but don't see that causing the problem. Looking today I couldn't locate the impulse hose - is it within the handle?

Basically, any other thoughts? I'll admit I just don't want it to be a carb thing as that's a pita, but does it actually sound like a carb thing seeing as it's been running well generally? All I can think of now other than the carb is the fuel line is blocked perhaps. Quite a bit of disassembly to check that out but might have to. 

Just want to be getting on with things really! 

Any advice gratefully received...

Cheers

[pleasant]

Well, if it is a 'carb thing' then this model is really easy to work on, and even the pattern carbs for 20 quid or so are pretty good. Whip the exhaust off and have a look at the piston, that would be my next logical step. Symptoms seem lean mix due to poor compression or air leak...possibly crank seals. But exhaust off and take a look at the condition of the piston next

Edited December 11, 2023 by pleasant

[Welshfred]

Thanks. I'll look further today. Air leak sounds feasible. I'll check out the piston but am now also considering the hose between carb and cylinder. I had forgotten on a previous saw that rubber caused a problem with air leaking. Don't remember the symptoms though, it was years ago...

[Welshfred]

Resolved. Fuel hose disconnected from cylinder. I'm surprised it was firing at all.... Starting issues appear sorted too.

[Muddy42]

3 hours ago, Welshfred said:

Resolved. Fuel hose disconnected from cylinder. I'm surprised it was firing at all.... Starting issues appear sorted too.

Do you mean fuel hose disconnected from the carb or impulse line disconnected from the cylinder?  Either way glad you got it sorted

[GarethM]

Also check the little rubber mounts between the fuel tank and the upper carb.

[spudulike]

It will be the impulse line pulled from the cylinder. I once had three MS260s in over two weeks and ALL had the same issue as this one with similar symptoms. 

An easy fix and usually happens when the bar gets compressed in the cut and the operator gets a bit enthusiastic pulling it out.

As Gareth said - check the AV mounts on the machine to make sure they haven't failed and made this happen.

Swap the impulse line out on the next full service. 

[adw]

Damn strange it would run a tank of fuel no problem, no convinced.

[Welshfred]

Thanks all. Yes, I imagine it is the impulse line then. The AVs are a bit baggy but not split. A changeout is prob a good idea, there's a bit more flex in the saw than there should be and I may well have wrenched it around a bit. With hindsight I probably didn't finish the tank of fuel just thought I had when the line got pulled and the saw stopped. As soon as I shone a torch in there today I spotted the issue.

As a side note those AVs don't seem to last very long.

[spudulike]

12 minutes ago, adw said:

Damn strange it would run a tank of fuel no problem, no convinced.

Not again, I will carry on calling you Doubting Thomas!!